This invention generally relates to a liner assembly for reducing emitted noise propagating through a duct. More particularly, this invention relates to a method of fabricating an acoustic liner with improved acoustic and operational performance.
During operation, an aircraft propulsion system generates noise that requires attenuation and control. The noise generated by operation of the aircraft propulsion system is of many different frequencies, some of which contribute disproportionately more noise to the overall emitted noise. Accordingly, the aircraft propulsion system is provided with a noise attenuation liner. Ideally, the noise attenuation liner will reduce or eliminate noise of all frequencies generated within the propulsion system. However, practical limitations reduce the efficient attenuation of noise at some frequencies in favor of other noise frequencies.
For these reasons, noise attenuation liners are tuned or tailored to attenuate the most undesirable frequencies with the greatest efficiency. Unfortunately, the compromises required to efficiently attenuate the most undesirable frequencies limits the effective attenuation of other noise frequencies.
Conventional acoustic liners include a cellular structure sandwiched between a back sheet and a face sheet including a plurality of openings. The openings create aerodynamic drag on the propulsion system during operation. The drag inhibits overall propulsion system performance. A known improvement is the use of woven mesh to cover the face sheet. The woven mesh provides a desirably low skin friction coefficient that reduces drag. Further, the woven mesh provides effective noise attenuation over a broad range of noise frequencies. Disadvantageously, a woven-mesh liner does not provide the desired durability and therefore requires increased maintenance at a prohibitive cost.
Accordingly, it is desirable to design and develop a noise attenuation liner and method of fabricating a noise attenuation liner that provides the durability desired, with reduced drag and increased frequency attenuation ranges.